Atrial fibrillation is an irregular heart rhythm that adversely affects approximately 2.5 million people in the United States. It is believed that at least one-third of all atrial fibrillation originates near the ostium of the pulmonary veins. Anatomically, two pairs of pulmonary veins are connected to the left atrium of the heart with each pair delivering blood to the heart from one of the patient's lungs.
It is further believed that the optimal technique to treat atrial fibrillation is to create circumferential lesions around the ostia where a pulmonary vein connects with the left atrium. More specifically, the goal is to ablate tissue to form a conduction block to thereby prohibit the transmission of irregular electrical signals that can cause an arrhythmia. To be effective, the conduction block must completely block irregular signals and this often requires the ablation of a relatively deep, uniform lesion. In some cases, more than one pulmonary vein must be treated to cure an arrhythmia.
To create circumferential lesions around the ostia using cryoablation, a typical procedure involves contacting tissue around the periphery of an ostium with a cryo-element and then cooling the cryo-element to ablate the contacted tissue. In some cases, the cryo-element can be hoop shaped allowing for a single-contact cryoablation. In other cases, a cryo-element that is arcuate, partially hoop shaped or dome shaped can be used. For such cryo-elements, multiple, successive contacts between the cryo-element and tissue are typically required. More specifically, these procedures require the cryo-element to be successively moved around the ostia to create a continuous ablation band.
For all of these types of cryo-elements, it is necessary to articulate the distal end of the catheter with great accuracy to aim and direct the cryo-element into contact with the targeted tissue. Moreover, this manipulation typically must be performed within a relatively limited space (e.g. the left atrium). For this purpose, it is desirable to be able to deflect the distal end of the catheter in more than one direction. With bi-directional capability, the distal end of the catheter can be deflected in a first direction (e.g. upward) to treat a first pulmonary vein, for example, and subsequently deflected in a second direction (e.g. downward) to treat a second vein. Furthermore, the ability to deflect the distal end of the catheter at relatively large deflection angles can potentially simplify and quicken many procedures.
In a typical bi-directional deflection system, a first pull wire is used to deflect the distal catheter tip in a first direction and second pull wire is provided to deflect the distal catheter tip in a second direction, opposite the first direction. For these conventional systems, a change in deflection from one direction to another can be problematic. For instance, when the tip is deflected a relatively small amount in the first direction, the second pull wire can typically be retracted to first straighten the catheter tip, and then deflect the tip in the second direction. However, when the deflection of the distal tip in the first direction is relatively large (e.g. ninety to one hundred eighty degrees or more), retraction of the second pull wire does not necessarily operate to smoothly recover the deflection and straighten the tip. Instead, for conventional bi-directional systems, retraction of the second wire can actually cause further deflection in the first direction and may prevent a deflection recover when the tension in the first wire is released.
In light of the above, it is an object of the present invention to provide a bi-directional system for actively deflecting a distal portion of a catheter while the distal portion is positioned within a body conduit. It is another object of the present invention to provide a system for bi-directionally controlling the cryo-tip of a cryoablation catheter that transitions from one direction to another with the operation of a single control knob. It is yet another object of the present invention to provide a system for bi-directionally controlling the cryo-tip of a cryoablation catheter that actively controls the amount of tip deflection in both directions and can hold the deflected cryo-tip in place. Yet another object of the present invention is to provide a bi-direction control system which is easy to use, relatively simple to implement, and comparatively cost effective.